AQL sampling: sample sizes and accept or reject
Agree the inspection lot, defect classes, inspection level and AQL before sampling. Use the lot size to find the code letter, then read the sample size and acceptance and rejection limits for each class. Record the counts separately before approving shipment. Cambridge China Bridge can coordinate this with its staff in China.
Define the lot before choosing the sample
Start with the goods actually presented for inspection, rather than the total purchase order. Ask the factory to identify the product, version, production batch and packed quantity. For mixed products or production runs, agree whether separate lots need separate decisions. Do not let good results for an unrelated product conceal problems in another.
Write down what counts as an inspected unit: the individual product, a retail set or another agreed unit. Give the inspector a defect list with photographs, measurement limits and functional checks. Use our product specification guide to prepare that brief; our inspection guide covers when to inspect.
Turn lot size into a sampling plan
For normal inspection with a single sample, find the lot-size row and inspection level to obtain the code letter. Then read the sample size and acceptance and rejection numbers under the agreed AQL. Our AQL sampling calculator provides those lookups. If an arrow moves the plan, use the sample size on the destination row.
Inspection level and AQL are separate choices. General inspection level II is the calculator's default; level I uses smaller samples and level III larger ones. Record the standard edition and inspection regime in the brief. The calculator covers normal single sampling; tightened or reduced inspection and other sampling arrangements need their own tables.
Worked examples: read the boundary correctly
For a lot of 3,200 units at general inspection level II, normal single sampling and AQL 2.5, the code letter is K and the sample is 125 units. Accept that defect class with 7 or fewer defective units; reject it at 8 or more. Finding 7 major-defective units therefore passes the major-defect check, but critical and minor results still need separate decisions.
For a lot of 3,201 units under the same settings, the code letter becomes L and the sample becomes 200 units. Accept with 10 or fewer defective units; reject at 11 or more. Do not carry the previous lot's sample size forward without checking. These examples illustrate the calculator's plans, rather than prescribing suitable limits for every product.
Choose limits around the consequence of failure
A common consumer-goods starting point is zero tolerance for critical defects, AQL 2.5 for major defects and AQL 4.0 for minor defects. These are agreed purchasing limits, not universal settings required by the standard. Treat unsafe defects as critical; distinguish failures affecting use or customer acceptance from tolerable cosmetic imperfections.
Classify actual examples before production: an exposed sharp edge, a failed closure and a faint surface mark may need different treatment depending on the product. Consider intended use, customer expectations and the cost of failure before choosing limits. State that finding a critical defect stops shipment approval. Do not treat finding none in the sample as proof that every unit is safe.
Make the report support a shipment decision
Ask the inspector to select goods across the lot rather than inspect a factory-prepared display. For the defective-unit plans illustrated here, record defective units by class rather than substitute a tally of individual blemishes. Agree how overlapping defect classes will be recorded. Ask for the lot identity, sample size, limits, counts and photographs in the report.
On failure, hold shipment approval and agree sorting, rework or rejection before arranging re-inspection. Do not keep drawing fresh samples until a favourable result appears. Ask what caused the failure and what changed in the goods or process. For repeated problems, use our guide to supplier quality slipping.
Frequently asked questions
Does AQL 2.5 mean I can accept that percentage faulty?
Use AQL 2.5 to look up the agreed plan's acceptance and rejection counts. Do not replace those counts with a percentage calculation on the shipment.
What sample size do I need for 3,200 units?
At general inspection level II, normal single sampling and AQL 2.5, inspect 125 units. Accept that defect class at 7 or fewer defective units and reject at 8 or more.
Which AQL should I use for critical defects?
Agree zero tolerance for critical defects and define them explicitly. Make any critical finding a stop for shipment approval, and agree the checks needed for the relevant hazards.
Can I take another sample after an AQL failure?
Agree corrective action and a re-inspection plan first. Avoid repeated sampling of an unchanged lot merely to obtain a pass; keep the failed report and evidence of the correction.